The present invention relates to a reciprocal hermetic compressor, and more particularly, to a dual cylinder apparatus for a reciprocal hermetic compressor.
Generally, as shown in FIG. 1, a reciprocal hermetic compressor includes a motor unit 1 having a stator 2, a rotor 4 rotatably disposed around the stator 2, a crankshaft 6, a connecting rod 8 and a cylinder apparatus 10.
The crankshaft 6 is connected to and rotated with the rotor 4, and has an eccentric portion 6a formed at a lower portion. The eccentric portion 6a is connected to a large diameter portion 8a formed on an end of the connecting rod 8. A small diameter portion 8b is formed on the other end of the connecting rod 8, and is connected to a piston 9.
As shown in FIG. 2, the cylinder apparatus 10 includes a cylinder body 111 in which the piston 9 is reciprocally inserted, a cylinder head 13 provided on one side of the cylinder body 11, and a valve plate 15 disposed between the cylinder body 11 and the cylinder head 13. The valve plate 15 has a refrigerant discharge hole 15a which is opened and closed by a discharge valve 16, and a refrigerant suction hole 15b which is opened and closed by a suction valve 17.
In the above-described invention, the piston 9 is reciprocated by the movement of the connecting rod 8, which compresses and expands the refrigerant inside of a cylinder chamber 11a. When the piston 9 retreats, the suction valve 17 is opened and the discharge valve 16 is closed. Accordingly, the refrigerant is drawn into the cylinder chamber 11a. When the piston 9 advances, the suction valve 17 is closed and the discharge valve 16 is opened. As a result, the refrigerant inside of the cylinder chamber 11a is compressed and discharged.
The above structure is an example of a cylinder apparatus in which the refrigerant is drawn into and then discharged from the cylinder body 11 during every one rotation of the crankshaft 6. This type of cylinder apparatus has a relatively low efficiency and increased noise level due to the vibration and unbalanced refrigerant suction/discharge.
Accordingly, it is an object of the present invention to provide a cylinder apparatus for a hermetic compressor, having an improved structure in which refrigerant discharge and suction are performed twice during one rotation of a crankshaft.
The above object is accomplished by providing a dual cylinder apparatus for a reciprocal hermetic compressor comprising a cylinder body having two open ends with a pair of valve plate units disposed at both ends of the cylinder body, the valve plate units having refrigerant discharge holes formed therein. A pair of pistons are movably disposed in the cylinder body to reciprocate inside of the cylinder body. A piston bar having one end connected to a connecting rod is slidably supported on the valve plate units to reciprocate thereon while supporting the pistons. The piston bar includes a refrigerant discharge hole through which a refrigerant is discharged from in between the pistons to outside the pistons. A discharge valve is movably disposed between the pistons, the discharge valve opening a first gap between one of the pistons and the cylinder body and closing a second gap between the other piston and cylinder body.
The pair of pistons are connected to the piston bar at a predetermined distance from each other, with each having a diameter smaller than an inner diameter of the cylinder body.
The pair of valve plate units include valve plates connected at both ends of the cylinder body to close the ends, the valve plates having refrigerant discharge holes and suction valves disposed on their opposing inner surfaces to selectively open and close the refrigerant discharge holes, according to an advancement and a retreat of the pistons.
The discharge valve includes a pair of ring-type valves movably disposed between the pair of pistons in close contact with an inner surface of the cylinder body. Springs connect the ring-type valves such that the ring-type valves are moved closer or further away from each other by an external pressure. The ring-type valves are compressed during both the advancement and retreat of the pistons, opening the first gap between one of the pistons and an inner surface of the cylinder body, while closing the second gap between the other piston and inner surface of the cylinder body. Each ring-type valve has a diameter that is greater than the diameter of the pair of pistons so that the ring-type valve can seal the gap between the piston and the inner surface of the cylinder body.